In recent years wood and coal burning stoves have gained widespread popularity as a means of home heating. These stoves operate efficiently and for long periods in a slow combustion mode. The joints of the stove are tightly sealed and air flow into the stove is carefully controlled. Such slow burning stoves provide high efficiency, but are subject to soot and creosote build-up in the stove itself and in the chimney or stovepipe.
Users frequently wish to be able to view the fire in a wood stove in a manner similar to an open fireplace. In order to control the air flow to the stove, it is necessary to provide transparent glass panels for viewing. During slow combustion in a wood stove, soot and creosote are deposited on all or parts of the transparent glass panels, thereby blocking the view of the fire. Once soot and creosote deposits occur, they are difficult to remove.
The transparent viewing panels are particularly difficult to keep clean when the stove is operated at low heat output. Wood stoves typically have a wide range of heat outputs, for example, 15,000-50,000 BTU per hour, but are customarily operated at low heat outputs to maintain comfortable temperatures for long periods while conserving fuel. Higher heat outputs are used during startup and during extremely cold weather conditions. Under high heat output conditions, operating temperatures are sufficiently high to prevent soot and creosote buildup on the glass panel interior. However, during low heat output conditions, stove surfaces are lower in temperature and deposit and condensation of soot and creosote on glass viewing panels are significant problems. It is desirable to provide a stove design wherein the transparent glass viewing panels will be kept uniformly clean and transparent throughout the life of the stove and over the range of operating conditions from low heat output to high heat output.
U.S. Pat. No. 4,461,273, Barker et al., discloses the use of incoming cool air directed downwardly over the transparent portion of the stove to reduce window temperature and resist staining and soot build-up thereon. U.S. Pat. No. 4,487,195, assigned to the assignee of the present invention, discloses a stove which utilizes air flow directed from each side and then upwardly across glass portions of a door to maintain those portions clean and unobscured. A gas exit from a primary combustion chamber is located relatively high on a rear wall of the chamber. European Patent Application No. 0047996 discloses a fireplace with glass doors utilizing laminar air flow of cool outside air from side channels across the inner surface of the glass doors. European Patent Application No. 0040100 discloses a stove with a viewing window wherein preheated air is delivered to the lower edge of the window. British Patent Application No. 2056052 discloses a heater provided with a viewing panel with openings at the top and bottom for flow of cool outside air across the inside of the viewing panel. A stove wherein outside air enters between dual pane glass doors is disclosed in Popular Science, Jan. 1982, p. 79. In general, such systems have not proven entirely satisfactory since soot and creosote build-ups still occur to some extent over portions of the glass window, particularly at low heat outputs.
It is a general object of the present invention to provide a heating apparatus with a glass panel which is maintained clean and transparent at all times.
It is another object of the present invention to provide a heating apparatus with a glass panel including means for supplying a curtain of hot air flowing uniformly and downwardly over the interior surface of the glass panel for elevating the glass temperature and forming a barrier to soot and creosote.
It is a further object of the present invention to provide a heating apparatus wherein a glass viewing panel is maintained clean over the entire range of heat outputs.
It is a further object of the present invention to provide a heating apparatus with a glass viewing panel and a system of internal manifolds for preheating of air, for removing turbulence and for directing a uniform curtain of hot air downwardly over the glass panel.
It is a further object of the present invention to provide a heating apparatus with glass viewing panels and a curtain of uniformly flowing air directed over the glass panels and then redirected into the combustion region such that combustion near the glass panels is maximized and such that radiation from the combustion region elevates the glass panel temperature.
It is a further object of the present invention to provide a wood burning stove with a transparent glass panel for viewing the fire, having a combination of the above-described features which combine effectively to minimize soot and creosote deposits on the glass panel.